The present invention refers to a gear shift device for bicycles having at least one derailleur, a first body destined to be attached to a bicycle frame and a second body that can be displaced with respect to the first body to cause the selective engagement of a bicycle chain on a number of sprockets, to achieve the various gears of the device, the device comprising:
an electric actuator to drive the displacement of the second body of the derailleur,
electronic control means for controlling the electric actuator,
manually-operated activating means, connected to the electronic control means, to cause activation of the electric actuator in order to select the required gear,
means for detecting the position of the second body of the derailleur and for indicating the position to the control means, so as to permit the automatic disabling of the electric actuator once the required position has been reached,
in which the electric actuator is directly associated with the derailleur.
A gear shift device of the kind outlined above is described and illustrated in U.S. Pat. No. 5,480,356, a patent held by the same applicant.
FIG. 1 of the attached drawings illustrates a racing bicycle, indicated as a whole by reference number 1, comprising a frame 2 constructed, in a well-known manner, of tubular elements comprising stays 3 for supporting the rear wheel 4. Reference number 5 indicates a fork for supporting a front wheel 6, associated with a handlebar 70, which is also made with a tubular structure.
In its lower part, the frame 2 carries a crankset 7 of substantially conventional type for driving the rear wheel 4 by means of a gear shift device made according to the present invention, indicated globally by the number 8.
The gear shift device 8 essentially includes a rear assembly 9 and a front assembly 10 comprised, in a well-known manner, of a number of sprockets 11 of various diameters, co-axial with the axle A of the rear wheel 4, and a number of crown wheels 12, also of various diameters, co-axial with the axle B of the bicycle's crankset 7.
The sprockets 11 and the crown wheels 12 can be engaged selectively by a chain transmission forming a closed ring 13 to achieve the different gear ratios available by means of the gear shift device 8, by activating a rear derailleur 14 forming part of the rear assembly 9 and a front derailleur 15 belonging to the front assembly 10.
FIG. 2 in the enclosed drawings illustrates the rear derailleur 14 made according to the solution proposed in U.S. Pat. No. 5,480,356. The rear derailleur 14 includes a first body 16 that is designed to be attached to the bicycle frame and a second body 17 connected to the first body 16 by means of a parallelogram linkage comprising two arms 18 and 19, the ends of which are articulated at 20, 21 and 22, 23 to the two bodies 16 and 17. The second body 17 includes, in a well-known manner, a rocker arm 24 that carries the chain transmission wheels 25 and 26.
Reference number 27 indicates an electric actuator, in the form of an electric motor combined with a reduction gear 29, that is directly incorporated in the derailleur 14 to drive the displacement of the second body 17, and consequently also of the rocker arm 24, through the various engagement positions of the chain 3 with the sprockets 11.
FIG. 3 in the enclosed drawings illustrates the motor and reduction gear assembly 27 forming the object of the device described in U.S. Pat. No. 5,480,356. In the Figure, the body of the motor and reduction gear assembly 27, indicated as 28, is shown on a larger scale and in cross-section. The body 28 contains not only the motor 35, but also an epicycloid reduction gear 29 connected to the shaft coming from the electric motor 35. The epicycloid reduction gear 29 drives the rotation of a screw 30. As shown in FIG. 2, the body 28 of the motor and reduction gear assembly is attached with an articulated coupling to the body 16 of the derailleur around an axis 22, while the screw 30 engages a nut screw 31, the body of which is mounted in an articulated manner around an axis 21 on the body 17 of the derailleur. As a result, the motor and gear reduction assembly lies along a diagonal of the parallelogram linkage and the turning of the motor causes a corresponding rotation of the screw 30 by the epicycloid gearing 29, so that the nut screw 31 moves along the screw, leading to an elongation or shortening of the distance between the axes 21 and 22 of the parallelogram linkage.
As illustrated in FIG. 3, the body 28 of the motor and reduction gear assembly also contains a device 32 comprising an encoder, including an optical or magnetic sensor that co-operates in a well-known manner with a disc 34 carried by the screw 30.
The electric power to the motor and reduction gear assembly 27 is provided by means of a battery 37 (FIG. 1) conveniently housed in one of the tubes of the bicycle frame 2 or, alternatively, in one side of the handlebar 70, or inside the container of a microprocessor control unit 40 (only partially visible in FIG. 1) that may be attached, for instance, to the bicycle frame in the area of the crankset and is used to control the electric motor 35 on the basis of signals originating from two manually-operated control levers 43 and 44 (which could also be replaced by two buttons) associated, in a well-known manner, with a brake lever 41 (FIG. 1). The microprocessor unit 40 is also connected to the encoder 32, which detects the angular position of the screw 30, and consequently of the rear derailleur, so as to stop the electric motor when a required transmission gear has been reached, the gear being selected by manually operating the levers 43 and 44 (which are operated to shift the chain into higher or lower gears, respectively). The connections between the aforementioned electric components are made, in the case of the above-mentioned well-known solution, by means of wires (not shown in the drawings) conveniently positioned inside the tubes of the bicycle frame 2.
The above-mentioned earlier document describes the opportunity to use an encoder of any kind to provide the means for detecting the position of the second body of the derailleur. In the course of experience gained in the past by the applicant, an incremental encoder was used. With this type of transducer, however, any interruption in the electric power supply to the encoder made it necessary to provide for a procedure for re-calibrating the encoder by making the derailleur move to the position taken as the zero reference by the encoder. It is also important to bear in mind that there is an increasingly-felt need to increase the autonomy of the bicycle with battery-powered systems and therefore to reduce the consumption of electrical energy. For this purpose, control systems can be used that enable energy to be delivered only for the amount of time it takes to satisfy the requirement, after which the system returns to a low-consumption regime. It is also true that, even using an incremental transducer, strategies can be adopted to keep the position value detected memorized at logic level in the control unit. However, this solution may not be sufficient to guarantee the reliability of the transducer, because while it is not being powered the position of the second body of the derailleur may undergo small variations due to the vibrations to which the bicycle is liable while in motion.